Many manufacturing processes involve the electroplating of copper on various surfaces including metal and conducting surfaces. Such copper platings are used to prevent corrosion, to increase electrical conductivity or thermal conductivity and to serve as an adherent layer for additional metallic layers. Recently, much activity with regard to copper electroplating has been associated with the production of various electronic circuits and devices including circuit boards, integrated circuits, electrical contact surfaces, etc.
Traditional electroplating processes for copper involve the use of a consumable counterelectrodes (or anodes). Here, the counterelectrode is made of metallic copper which is oxidized to soluble copper ions during the electroplating process. The counterelectrodes serve not only as the anode in the electroplating process but also as a source of copper ions in the electroplating bath to replace the copper ions consumed in the electroplating process at the cathode.
The copper electroplating process described in the instant application involves use of nonconsumable counterelectrode. Such processes are advantageous because of potentially higher plating rates, better control of bath chemistry, smaller plating apparatus size and use of various copper salts (such as copper oxide) as sources of copper in the electroplating process. These copper salts are often readily available from etching procedures in the manufacture of various electronic circuit boards.
Particularly important in electroplating processes with nonconsumable anodes is the structure and surface composition of the anode. The nature of the anode often determines (or at least greatly influences) the efficiency of the process, the nature of side reactions at the anode, the nature of the resulting deposit and the lifetime of the plating bath.
The composition of electrodes for various electrochemical processes have been described extensively in the literature. Particular references are as follows: U.S. Pat. Nos. 3,428,544 (Guiseppe Bianchi et al, issued Feb. 18, 1969); 3,491,014 (Guiseppe Bianchi et al, issued Jan. 20, 1970); 3,616,445 (Guiseppe Bianchi, issued Oct. 26, 1971); and Extended Abstracts of the Electrochemical Society Spring Meeting, Seattle, Washington, May 21-26, 1978, Volume 78-1, pp. 1202-1205. In addition, two patents by H. B. Beer (U.S. Pat. No. 3,632,498 issued on Jan. 4, 1972 and 3,711,385 issued on Jan. 16, 1973) are of interest. Also, several references are of interest in connection with anodes used for gold plating. These are U.S. Pat. Nos. 4,067,783 issued on Jan. 10, 1978 to Okinaka et al; 4,269,670 issued to C. G. Smith on May 26, 1981, and a patent application with inventors Y. Okinaka and C. G. Smith, filed Dec. 21, 1979 with Ser. No. 105,977 and now U.S. Pat. No. 4,310,391.